Production of a semiconductor device involves a step of forming an electroconductive film on the surface of a wafer to form a wiring layer by photolithography, etching etc., a step of forming an interlaminar insulating film on the wiring layer, etc., and an uneven surface made of an electroconductive material such as metal and an insulating material is generated on the surface of a wafer by these steps. In recent years, processing for fine wiring and multilayer wiring is advancing for the purpose of higher integration of semiconductor integrated circuits, and accordingly techniques of planarizing an uneven surface of a wafer have become important.
As the method of planarizing an uneven surface of a wafer, a CMP method is generally used. CMP is a technique wherein while the surface of a wafer to be polished is pressed against a polishing surface of a polishing pad, the surface of the wafer is polished with slurry having abrasive grains dispersed therein. As shown in FIG. 1, a polishing apparatus used generally in CMP is provided for example with a polishing platen 2 for supporting a polishing pad 1, a supporting stand (polishing head) 5 for supporting a polished material (wafer) 4, a backing material for uniformly pressurizing a wafer, and a mechanism of feeding an abrasive. The polishing pad 1 is fitted with the polishing platen 2 for example via a double-sided tape. The polishing platen 2 and the supporting stand 5 are provided with rotating shafts 6 and 7 respectively and are arranged such that the polishing pad 1 and the polished material 4, both of which are supported by them, are opposed to each other. The supporting stand 5 is provided with a pressurizing mechanism for pushing the polished material 4 against the polishing pad 1.
Conventional polishing pads for use in high-precision polishing are generally produced using a polyurethane resin foam sheet. Unfortunately, such a polyurethane resin foam sheet has insufficient cushioning properties and therefore can hardly apply uniform pressure to the entire surface of a wafer, though it has high local-planarization performance. In general, therefore, a soft cushion layer is additionally provided on the back side of such a polyurethane resin foam sheet, and the resulting laminated polishing pad is used for polishing.
However, conventional laminated polishing pads have the problem that since a polishing layer and a cushion layer are usually bonded to each other by a double-sided tape, a slurry infiltrates between the polishing layer and the cushion layer during polishing, or durability of the double-sided tape is reduced by heat generated during polishing (the pad surface temperature rises to about 80° C. in the case where a ceria slurry is used or the case of metal polishing), so that the polishing layer and the cushion layer are easily peeled from each other.
Examples of proposed methods to solve this problem include the techniques described below.
Patent Document 1 discloses a method for producing a multiple-layer chemical mechanical polishing pad, including disposing an uncured reactive hot-melt adhesive between a polishing layer and a sub-pad layer, and pressing the two layers against each other to cure the uncured reactive hot-melt adhesive, thereby forming a reactive hot-melt adhesive bond between the two layers.
Patent Document 2 discloses a polishing pad in which a polishing layer and a lower layer are joined to each other with a hot-melt adhesive containing EVA.
Patent Document 3 discloses a polishing pad formed by bonding and laminating a polishing layer, which includes a fabric or open-type lattice structure having an aperture of 10 to 100 μm, to a support with an adhesive layer of a fused thermoplastic resin interposed therebetween.
However, if a polishing layer and a cushion layer are bonded to each other with a hot-melt adhesive as in conventional production methods, there is the problem that warpage easily occurs in the obtained laminated polishing pad.